Biocontrol with predatory mites: build up the army before the battle is on!

A strong standing army of predatory mites is a great way to protect your crop from pest attack. ”In the past, growers had to wait for pests to be present in the crop before releasing predatory mites. Without pests, predators had no food to survive. But giving the pest a head-start often means that the army arrives when the battle is already lost. With NutrimiteTM, a unique food for predatory mites introduced by Biobest in 2013, we generated a paradigm shift in biological control. For the first time predatory mites could be used preventatively. NutrimiteTM allows to build up large populations of predators before the pest arrives.” says Felix Wäckers, Biobest R&D director. We asked him to present a state of affairs 3 years after NutrimiteTM’s initial launch.

NutrimiteTM applications on the rise

“We see NutrimiteTM gaining ground in different crops and in combination with different predatory mites”, says Felix. “Predatory mites that respond strongly to supplementary feeding include A. swirskii, A. degenerans and, of course, Euseius gallicus. The latter species, which is marketed under the name Dyna-Mite® G-System, is a mite that shows a particularly explosive population growth in response to NutrimiteTM. We’ve developed tailor-made strategies for different crops. To name a few examples: in roses, the combination of Euseius gallicus with NutrimiteTM is a real game changer and is now being used commercially by many leading rose growers. In cucumber, growers in different parts of the world are very satisfied with the combination of A. swirskii and NutrimiteTM. More recently we have started to see big benefits with NutrimiteTM in pepper. Starting with NutrimiteTM before the crop is flowering allows good biological whitefly protection with A. swirskii from the very beginning of the crop cycle. It also allows to build a strong population of A. degenerans when thrips and spider mite are the main challenges. Interestingly, we even see strong NutrimiteTM benefits when the crop is flowering and produces pollen itself. This can be explained by the fact that predatory mites prefer NutrimiteTM over many other pollen types.”

Higher numbers, better distribution

Another advantage lies in the fact that NutrimiteTM is applied on all plant parts. That allows for a much better distribution of the predatory mites in the crop as compared to untreated crops where pollen is only present in the flowers. The resulting crop-wide distribution of predatory mites improves the chances that they come across pests like whitefly or spider mites. Also when we compare the use of NutrimiteTM to breeding sachets, the more even distribution is an important trump card. In the case of breeding sachets, predatory mite breeding is contained inside a small bag. When we use NutrimiteTM, the predators breed throughout the crop, and that is of course where they will encounter pests. To highlight this advantage we have coined the phrase: “breed them where you need them”.

NutrimiteTM – the right pollen for the job

Felix also has a lot to say when it comes to the crucial impact of pollen type and quality on the success of predatory mite feeding. “When developing NutrimiteTM we were specifically looking for a source of pollen that combines a high nutritional value to predatory mites with a low suitability to thrips pests.” Previous studies had already highlighted that the pollen used in NutrimiteTM is particularly suitable for predatory mites, while it is very low on the thrips menu preference.“Moreover, due to its production process and our logistics chain, we can guarantee that NutrimiteTM is fresh and totally free of pesticide residues. We’ve compared it to other predatory mite feeding products that have since been introduced in the market, and we’ve seen that NutrimiteTM stands out in terms of stimulating predatory mite numbers.”

Power in numbers

“We see statements out there claiming that applying NutrimiteTM is risky because it could cause populations of thrips to increase. I understand that some may see the NutrimiteTM concept as a threat to current release strategies, in which growers have to purchase and release more predatory mites. However, there are many independent studies that counter these concerns. Just look at the graph below, in which the impact of two pollen types on a predatory mite and on thrips, and you see how strongly the balance of NutrimiteTM is shifted towards feeding predators. As a result, NutrimiteTM stimulates predatory mite populations much more than thrips populations. And it is the ratio of predatory mites to thrips that ultimately determines the efficacy of pest control. That principle was already described in depth by Paul van Rijn, a Dutch researcher who is an internationally recognized expert in this field. The title of the 2002 paper sums it up nicely: how plants benefit from providing food to predators even when it is also edible to herbivores.”

Source: Van Rijn and Tanigoshi, 1999 in Experimental and Applied Acarology; Hulshof and Vänninen, 2003 in Proceedings of the 7th International Symposium on Thysanoptera.

When and how to feed NutrimiteTM?

Over the last few years, Biobest’s technical team has developed a wealth of experience with regard to dosage, application techniques and application frequency. Your Biobest advisor is best placed to provide tailor made advice. The most appropriate dose rate is usually 500 g/ha. Overall, most applications are done with the Makita in combination with the NutriApp. For small surfaces, a small manual blower is available. The goal of NutrimiteTM is to support the establishment of a strong predatory mite population in the absence of pests. In the absence of pest pressure, one application every two weeks will keep the predatory mite population in great shape. As with all biocontrol strategies, we always recommend careful monitoring. Once pest pressure has reached a certain level, the predatory mites will have an alternative food source and NutrimiteTM feeding can be put on hold.

More NutrimiteTM benefits

As we continue the research on NutrimiteTM, we’re seeing additional benefits of this strategy. One such benefit is the fact that NutrimiteTM reduces intraguild predation, the predation of predatory mites on other beneficials such as Aphidoletes. Another benefit is the finding that the negative impact of certain pesticides on predatory mites can be mitigated if NutrimiteTM is applied after the application. With growing experience in different crops and different countries, our advisors are able to help growers exploit the advantages of the new strategy to the fullest. Don’t hesitate to call on them for tailor-made advice.